A number of threading attachments such as tap drivers have been devised, including reversible units. Patents such as U.S. Pat. Nos. 3,002,206 and 3,717,892 have shown radial cylindrical pins fixed in the output member as the driven clutch element. Other prior art designs, such as U.S. Pat. Nos. 3,946,844; 3,999,642; 4,014,421 and 4,029,429, have utilized a three-part clutch with freely rolling balls in a cage sleeve, the balls acting between inner and outer splines.
These constructions are ones which require a high degree of precision in the machining or forming of the parts in order to have accurate alignment of the parts and in order to have adequate torque transmitting ability of the forward and reverse clutches. Such accuracy in machining is expensive to obtain.
The problem to be solved is how to obtain a threading attachment of the tap-driver type which is rugged yet maintains accurate alignment and which has a minimum of parts requiring accurate machining. Another problem to be solved is how to obtain smooth clutch engaging action for engagement of both the forward and reverse clutches.